Varro, De lingua latina 5.71: (Lympha Iuturna quae iuvaret: itaque multi aegroti propter id nomen hanc aquam petere solent). See also Frontinus, On Aqueducts 1.4, where Juturna is in company with the Camenae and Apollo. C. Bennett Pascal, The Cults of Cisalpine Gaul (Latomus, 1964), p. 93, reads an inscription as linking the Celtic godBelenus (usually identified with Apollo) and the Lymphae, but Dessau reads Nymphae (ILS 4867). Servius, note to Aeneid 12.139, has Juturna as a fons, and Propertius4.21.26, as the lympha salubris who restored a horse of Pollux (some editions emend to nympha; see note to the line at Sexti Aurelii Propertii Elegiarum Libri Quattuor, edited by N. Lemaire (1840), p. 448 online).
Isidore, Etymologies 4.6.12 and 10.L.161, as translated by Barney et al., pp. 110, 223. See also Festus, entry on Lymphae, p. 107 in the edition of Lindsay.
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Vitruvius, De architectura1.1.5, Bill Thayer's edition at LacusCurtius of the translation by Joseph Gwilt, The Architecture of Marcus Vitruvius Pollio (London, 1826). The Latin text at LacusCurtius is that of Valentin Rose's 1899 Teubner edition: Veneri Florae Proserpinae Fonti Lumphis corinthio genere constitutae aptas videbuntur habere proprietates, quod his diis propter teneritatem graciliora et florida foliisque et volutis ornata opera facta augere videbuntur iustum decorem. A textualcrux occurs at the relevant phrase: Gwilt translates Fontium Lumphis ("for the Lymphae of the Fountains"), but some editions give Fonti Lumphis ("for Fons, for the Lymphae").